Process for the preparation of a maltose-rich syrup

ABSTRACT

The present invention relates to a process for the preparation of a maltose-rich syrup comprising the steps of (a) carrying out liquefaction of a starch milk; (b) carrying out saccharification of the liquefied starch milk in the presence of a β-amylase and at least one debranching enzyme selected from the group comprising pullulanases and isoamylases; (c) carrying out molecular sieving of the liquefied and saccharified starch milk so as to collect a fraction enriched with maltose and a fraction enriched with glucose; and (d) bringing said fraction enriched with maltose into contact with a maltogenic α-amylase with a view to obtaining a maltose-rich syrup.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a Divisional patent application of U.S.patent application Ser. No. 09/473,381 filed Dec. 28, 1999, thedisclosure of which is being incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a process for the preparation of amaltose-rich syrup. It also relates to the use of a maltose-rich syrupobtained by the process according to the present invention for thepreparation of a maltitol-rich syrup. It also relates to the use of amaltose-rich syrup obtained by the process according to the presentinvention for the preparation of crystallised maltitol.

[0004] 2. Description of the Prior Art

[0005] Processes by which maltose-rich syrups can be obtained arealready well known. These processes include, in particular, the onedescribed by HODGE and co-workers in “Cereal Chemistry” no. 25, pages19-30, January 1948 and which comprises a step involving theprecipitation of limit dextrins by alcoholic solutions, and the onedescribed by WOLFROM and THOMPSON in “Methods in carbohydratechemistry”, 1962, pages 334-335.

[0006] Other processes for the preparation of maltose-rich syrups havealso been proposed comprising a step involving adsorption of dextrinsover carbon (U.S. Pat. No. 4,194,623), a step involving chromatographyover zeolites or cationic or anionic resins (FR-A-2.510.581), a stepinvolving ultrafiltration of maltose syrups (U.S. Pat. No. 4,429,122),the combined use of several different enzymes namely an α-amylase, aβ-amylase and an isoamylase or a pullulanase (FR-A-2.012.831).

[0007] This latter method has numerous advantages over the previousones. Nevertheless, it suffers from certain disadvantages including, inparticular, the fact that the saccharification operations have to becarried out with very low dry matter contents of the order of 20 g/l inorder to obtain maximum effectiveness of hydrolysis with enzymes.

[0008] The document FR-A-2.000.580 describes a process for thepreparation of a syrup with a high maltitol content by hydrogenation ofa syrup with a high maltose content which is obtained by liquefaction ofa starch milk with a low dry matter content to a dextrose equivalent ofless than 2, the product thus obtained being saccharified under theaction of specific enzymes.

[0009] This process is expensive, has a mediocre yield and gives rise toproblems of bacterial contamination and phenomena of retrogradation ofthe amylose. Moreover, the syrup obtained contains proportions ofpolymers with degrees of polymerisation (DP, in the descriptionhereinafter) greater than or equal to 4, which are troublesome.

[0010] More recently, the document U.S. Pat. No. 5,141,859 proposed aprocess for the preparation of a syrup with a high maltose contentemploying two successive saccharification steps. This documentadvocates, in fact, a process comprising a first saccharification stepin the presence of a β-amylase and a subsequent saccharification step inthe presence of a maltogenic α-amylase. According to this document, themaltogenic α-amylase is used after the first saccharification step toβ-amylase to hydrolyse the oligosaccharides (from DP3 to DP7) andessentially the maltotriose (trisaccharide) to maltose and glucose.

[0011] Although the use of maltogenic α-amylase makes it possible,effectively and advantageously, to lower the maltotriose proportion byhydrolysis of the latter to maltose and glucose, it nevertheless has themajor disadvantage of generating large quantities of glucose andpossibly sorbitol in the event of hydrogenation of the hydrolysates. Infact, a large proportion of glucose originating from the hydrolysis ofmaltotriose by the maltogenic α-amylase is added to the residual glucoseobtained after saccharification of the liquefied starch milk.

[0012] These large quantities of glucose, therefore of sorbitol afterhydrogenation, make the crystallisation of maltitol more difficult andlead to a reduction in the crystal content, making these crystalsill-suited to certain applications such as, for example, chocolateproduction.

[0013] Moreover, the persistence of free glucose or sorbitol in themaltose or maltitol syrups bring about other disadvantages such as areduction in the viscosity and equilibrium moisture content of theproducts in which they are incorporated as sugar substitutes.

[0014] Inasmuch as there is a growing interest in products with a veryhigh maltose content, there is a need for considerable research with aview to developing an economic and extremely reliable process forobtaining such products.

BRIEF SUMMARY OF THE INVENTION

[0015] In an extremely simple and particularly effective manner withregard to all the proposals to date, the present invention disclosesthat syrups with a very high maltose content could be prepared bycarrying out molecular sieving of a liquefied and saccharified starchmilk so as to collect a fraction enriched with maltose and a fractionenriched with glucose, then bringing said fraction enriched with maltoseinto contact with a maltogenic α-amylase.

[0016] The invention proposes, therefore, a process for the preparationof a maltose-rich syrup comprising the successive steps consisting in:

[0017] (a) carrying out liquefaction of a starch milk;

[0018] (b) carrying out saccharification of the liquefied starch milk inthe presence of a β-amylase and at least one debranching enzyme selectedfrom the group comprising pullulanases and isoamylases;

[0019] (c) carrying out molecular sieving of the liquefied andsaccharified starch milk so as to collect a fraction enriched withmaltose and a fraction enriched with glucose;

[0020] (d) bringing said fraction enriched with maltose into contactwith a maltogenic α-amylase with a view to obtaining a maltose-richsyrup.

[0021] The invention also proposes a process for the preparation of amaltose-rich syrup comprising the successive steps consisting in:

[0022] (a) carrying out liquefaction of a starch milk;

[0023] (b) carrying out saccharification of the liquefied starch milk inthe presence of a β-amylase;

[0024] (c) carrying out molecular sieving of the liquefied andsaccharified starch milk so as to collect a fraction enriched withmaltose and a fraction enriched with glucose;

[0025] (d) bringing said fraction enriched with maltose into contactwith a maltogenic α-amylase and at least one debranching enzyme selectedfrom the group comprising pullulanases and isoamylases with a view toobtaining a maltose-rich syrup.

[0026] The process for the preparation of a maltose syrup which is theobject of the present invention is based in fact on a simple observationwhich has been neglected hitherto whereby the action of a specificenzyme on a given substrate is effective only if the characteristics assuch of the substrate effectively permit the action thereof.

[0027] In the present case, an effective action of maltogenic α-amylasemay be obtained only from a liquefied and saccharified starch milkhaving a particular composition, having in particular a bimodalcarbohydrate spectrum, namely having, apart from a high maltose and anappreciably high oligosaccharide content, a high glucose content.

[0028] The present invention seeks therefore, to ensure that theimpurities are in the form of glucose rather than in the form ofoligosaccharides, and in particular maltotriose, with a molecular massclose to that of maltose.

[0029] The particular bimodal carbohydrate spectrum of the liquefied andsaccharified starch milk is obtained according to the process of theinvention by carrying out a molecular sieving step on the latter.

DETAILED DESCRIPTION OF THE INVENTION

[0030] The first step of the process according to the invention isinherently known. It consists in liquefying a starch milk of anybotanical origin; it may originate from wheat, corn or potato, forexample.

[0031] Acid is added to this starch milk in the case of so-called acidliquefaction, or an α-amylase is added in the case of enzymaticliquefaction.

[0032] In the process according to the invention, it is preferable tocarry out controlled hydrolysis of the starch milk so as to obtain aliquefied starch milk with a low degree of conversion. Thus, theconditions of temperature, pH, enzyme and calcium level known to theskilled person are determined in such a way that they make it possibleto obtain a DE (dextrose equivalent) of less than 10, preferably lessthan 6, and more particularly less than 4. Preferably, the liquefactionstep is carried out in two sub-steps, the first consisting in heatingthe starch milk for a few minutes and to a temperature in the range 105°C. to 108° C. in the presence of an α-amylase (TERMAMYL® 120L type soldby NOVO) and a calcium-based activator, the second consisting in heatingthe starch milk thus treated to a temperature in the range 95° C. to100° C. for one to two hours.

[0033] Once the liquefaction step has ended, under conditions of drymatter content, pH, enzyme and calcium level that are well known to theskilled person, inhibition of the α-amylase is carried out. Thisα-amylase inhibition may take place preferably by thermal means bycarrying out a thermal shock of a few seconds at a temperature greaterthan or equal to 130° C. at the outlet of liquefaction.

[0034] Saccharification of the liquefied starch milk is then carried outby means of a β-amylase such as that sold by GENENCOR under the nameSPEZYME® BBA 1500.

[0035] During this step, it is advisable to combine the β-amylase withan enzyme which specifically hydrolyses the α-1,6 bonds of the starch.This addition of a debranching enzyme makes it possible on the one handto accelerate the hydrolysis reactions without simultaneouslyaccelerating the reversion reactions and, on the other hand, to reducethe quantity of highly branched oligosaccharides normally resistant tothe action of maltogenic enzymes.

[0036] This addition of debranching enzyme may take place at the time ofthe addition of β-amylase or at the time of the addition of maltogenicα-amylase.

[0037] According to the invention, the debranching enzyme is selectedfrom the group comprising pullulanases and isoamylases. An example ofpullulanase is that sold by ABM under the name PULLUZYME® 750L. Anexample of isoamylase is that sold by HAYASHIBARA.

[0038] Advantageously, the process according to the invention is carriedout in the presence of isoamylase, the Applicant company having observedthat said isoamylase made it possible to obtain a maltose syrup having ahigher maltose content than when pullulanase was used.

[0039] In a particular embodiment of the invention, the saccharificationstep may also be carried out wholly or partially in the presence offungal α-amylase, for example, SPEZYME® DBA 1500 (sold by GENENCOR)instead of SPEZYME® BBA 1500 (sold by the same company).

[0040] At the end of saccharification, it is possible to add a littleα-amylase which generally improves the subsequent filtration steps. Thequantities and conditions of action of the different enzymes used in theliquefaction and saccharification steps of the starch milk are generallythose which are recommended for the hydrolysis of starch and are wellknown to the skilled person.

[0041] Saccharification with β-amylase optionally combined with thedebranching enzyme is carried out until the maltose hydrolysate containsat least 75 wt. % of maltose and preferably about 80 wt. % of maltose.It lasts at least 24 hours.

[0042] The hydrolysate thus saccharified is then filtered over a precoatfilter or by microfiltration over membranes, then demineralised andconcentrated.

[0043] At this stage of the process according to the invention, theliquefied and saccharified starch milk undergoes molecular sieving inorder to collect a fraction enriched with maltose and a fractionenriched with glucose. After this, the fraction enriched with maltose isbrought into contact with a maltogenic α-amylase. This latter isadvantageously that sold by NOVO under the names Maltogenase® 4000L andNOVAMYL®.

[0044] The molecular sieving step used in the process according to theinvention may consist, for example, in a chromatographic separation stepor a step involving separation over membranes.

[0045] The chromatographic fractionation step is carried out in aninherently known way, batchwise or continuously (simulated mobile bed)over adsorbents of the cationic resin type or over strongly acidzeolites, loaded preferably using alkali or alkaline-earth ions such ascalcium or magnesium but more preferably using sodium ions.

[0046] Instead of the chromatographic separation step, it is possible,in the process according to the invention, to use a step involvingseparation by nanofiltration over membranes. Membranes of different porediameters are produced from numerous polymers and copolymers of thepolysulfone, polyamide, polyacrylonitrate, polycarbonate, polyfuran etc.type.

[0047] Examples of the use of such membranes are described in particularin the documents U.S. Pat. No. 4,511,654, U.S. Pat. No. 4,429,122 andWO-A-95/10627.

[0048] According to an advantageous embodiment of the process accordingto the invention, the non-maltose part derived from the membranes orfrom chromatography, comprising the fraction enriched with glucose, isrecycled upstream of the saccharification step.

[0049] By virtue of the process according to the invention whichbenefits from the advantages obtained both from the hydrolysis stepsused and from the molecular sieving step, it is possible to obtain, withyields greater than 90%, a starch hydrolysate whose maltose content isgreater than 95%, and even greater than 98% if an isoamylase is used inthe hydrolysis steps.

[0050] At this stage of the process according to the invention, it isoptionally possible to carry out a crystallisation of the maltose or acatalytic hydrogenation on the hydrolysate (or maltose syrup).

[0051] The hydrogenation of such a hydrolysate is carried out accordingto the rules of the art which lead, for example, to the production ofsorbitol from glucose.

[0052] It is equally possible to use catalysts based on ruthenium andRaney nickel catalysts for this step. It is preferable, however, to useRaney nickel catalysts which are less expensive.

[0053] In practice, 1 wt. % to 10 wt. % of catalyst is used based on thedry matter of the hydrolysate undergoing hydrogenation. Hydrogenation iscarried out preferably on a hydrolysate whose dry matter content is inthe range 15% to 50%, in practice around 30% to 45%, under a hydrogenpressure in the range 20 bars to 200 bars. It may be carried outcontinuously or batchwise.

[0054] If operations are carried out batchwise, the hydrogen pressureused is generally in the range 30 bars to 60 bars, and the temperatureat which hydrogenation takes place is in the range 100° C. to 150° C. Itis also important to maintain the pH of the hydrogenation medium byadding soda or sodium carbonate, for example, but without exceeding a pHof 9.0. This method of operating makes it possible to avoid theappearance of cracking or isomerisation products.

[0055] The reaction is terminated when the reducing sugar content of thereaction medium has become less than 1%, preferably less than 0.5% andmore particularly less than 0.1%.

[0056] After the reaction medium has been cooled, the catalyst isremoved by filtration and the maltitol syrup thus obtained isdemineralised over cationic and anionic resins. At this stage, thesyrups contain at least 93% maltitol.

[0057] The maltitol syrup obtained in the preceding hydrogenation stepmay then undergo a crystallisation step in order to obtain crystallisedmaltitol.

[0058] According to a preferred embodiment according to the invention,the maltitol syrup obtained in the preceding hydrogenation step is used,the succession of following steps consisting in:

[0059] concentrating the maltitol syrup;

[0060] crystallising and separating the maltitol crystals formed;

[0061] carrying out molecular sieving on the crystallisation motherliquors and, in particular, chromatographic fractionation so as toobtain a maltitol-rich fraction and a maltitol-poor fraction;

[0062] recycling the maltitol-rich fraction upstream of thecrystallisation step;

[0063] optionally carrying out acid hydrolysis and/or enzymatichydrolysis on the maltitol-poor fraction using, for example, animmobilised or non-immobilised amyloglucosidase;

[0064] optionally carrying out hydrogenation of said hydrolysedmaltitol-poor fraction in order to obtain a sorbitol syrup.

[0065] Surprisingly and unexpectedly, the use according to the inventionof a maltose-rich syrup for the preparation of crystallised maltitolmakes it possible to reduce very substantially (up to 80% compared witha conventional process) the quantities of mother liquors (i.e. themaltitol-poor fraction) produced during the molecular sieving stepdownstream of the crystallisation step.

[0066] Other features and advantages of the invention will become clearon reading the examples that follow. They are given here, however, onlyby way of non-limiting example.

EXAMPLE 1

[0067] A starch milk with a dry matter content of 31% is liquefied inthe conventional way using 0.2% TERMAMYL® 120L (α-amylase sold by NOVO)at a pH of 5.7 to 6.5 to a DE slightly below 4.

[0068] The reaction medium is then heated for a few seconds to 140° C.in order to inhibit the α-amylase, then the pH is adjusted to between 5and 5.5 and the temperature to 55° C.

[0069] Saccharification is carried out to a dry matter content of 25% orslightly below, in the presence of pullulanase (PULLUZYME® 750L sold byABM) and β-amylase (SPEZYME® BBA sold by GENENCOR) in respective amountsof 0.1% and 0.05% based on dry matter.

[0070] Saccharification, which lasts about 48 hours, gives a hydrolysatehaving the following composition. DP1: 1.4%, DP2: 82.4%, DP3: 13.2%, DP4and above: 2.6%.

[0071] The hydrolysate then undergoes conventional purification byfiltration, bleaching and demineralisation and is then concentrated toabout 20% of dry matter and adjusted to a pH of 5.5.

[0072] A step involving the continuous chromatography of the maltosehydrolysate thus obtained is carried out in the following manner.

[0073] Four columns of a liter of resin PCR 732 in the sodium formthermostated to 75° C. are assembled in series and fed continuously withthe maltose hydrolysate brought to a dry matter content of 60 wt. %, ata flow rate of 110 ml/h.

[0074] The fractions enriched with maltose having the followingcomposition are recovered at the outlet of the column:

[0075] DP1: 1.5%, DP2: 94%, DP3: 4.5%.

[0076] The chromatographic maltose yield is 91.5%.

[0077] These fractions are concentrated to about 20% of dry matter andadjusted to a pH of 5.5 then brought into contact with a maltogenicα-amylase (Maltogenase® 4000L sold by NOVO) in a quantity of 0.3% basedon dry matter. The composition of the maltose syrup obtained is asfollows: DP1: 4%, DP2: 95.5%, DP3: 0.5%.

EXAMPLE 2

[0078] The maltose syrup obtained in example 1 above undergoes a maltosecrystallisation step in the following manner. A maltose solution with adry matter content of 75 wt. % is prepared at a temperature of 75° C.The maltose solution is seeded with 5 wt. % of maltose crystal seeds andthe solution is cooled from 75° C. to 40° C. at a rate of 0.5° C. perhour whilst agitating the solution at 50 rpm in a double-walledcrystalliser.

[0079] At the end of crystallisation, the crystals are separated fromthe mother liquor using a conventional centrifuge.

[0080] The crystallisation yield is 50 wt. % expressed in weight ofcrystallised maltose based on the starting weight of maltose.

[0081] The maltose purity of the crystals recovered is 97.5% based ondry matter. The water content is 5%.

EXAMPLE 3

[0082] The maltose syrup obtained from example 1 is demineralised thenhydrogenated under the following conditions: Dry matter: 40%Temperature: 115° C. Amount of catalyst: 5 wt. %/dry matter H₂ pressure:50 bars

[0083] The reaction is terminated when the reducing sugars are less than0.3%. The medium is then filtered, demineralised and concentrated to 85%of dry matter; its composition is: Sorbitol:  5.5% Maltitol: 94.0%Higher hydrogenated products:  0.5%

[0084] The crystallisation step is then carried out by cooling from 75°C. to 25° C. at a rate of 0.5° C./hour under slow agitation, withinoculation with 6 wt. %/dry matter of crystallised maltitol with aparticle size in the range 200 μm to 250 μm.

[0085] After centrifuging, the crystals are dried and have a content of99.7%; the mother liquors are adjusted to 60% dry matter andchromatographed.

[0086] Four columns of one liter of resin PCR 732 in the calcium form,thermostated to 85° C. are assembled in series and fed continuously at arate of 120 ml/h. The maltitol yield is 90.7% and the rich fraction(maltitol-rich fraction) has the following composition: sorbitol 4.5%;maltitol 95%; higher hydrogenated products: 0.5%.

[0087] The maltitol-poor fraction containing 53.5% of sorbitol, 42.5% ofmaltitol and 4% of higher hydrogenated products then undergoes an acidhydrolysis step.

[0088] Hydrolysis of the maltitol-poor fraction is carried outcontinuously over a cation exchange resin of the Purolite C145 type inthe H′ form placed in a column thermostated to 115° C.; by feeding thecolumn at 1 bv/h¹ with the solution concentrated to 40%, the followingcomposition is obtained: sorbitol: 70.5%; maltitol: 12.3%; higherproducts: 0.4%, glucose: 16.8%.

[0089] This solution is then demineralised and hydrogenated under thefollowing conditions: dry matter: 40% temperature: 135° C. amount ofcatalyst: 5 wt. %/dry matter hydrogen pressure: 50 bars.

[0090] until a free reducing sugar content of less than 0.1% isobtained.

What is claimed is:
 1. A process for the preparation of a maltose-richsyrup comprising the successive steps of: (a) carrying out liquefactionof a starch milk; (b) carrying out saccharification of the liquefiedstarch milk in the presence of a β-amylase and at least one debranchingenzyme selected from the group comprising pullulanases and isoamylases;(c) carrying out molecular sieving of the liquefied and saccharifiedstarch milk so as to collect a fraction enriched in maltose and afraction enriched in glucose; (d) bringing said fraction enriched withmaltose into contact with a maltogenic α-amylase in order to obtain amaltose-rich syrup; and (e) crystallizing the maltose-rich syrup inorder to obtain a crystallized maltose.
 2. The process of claim 1further including the step of hydrogenating the maltose-rich syrup inorder to obtain a maltitol rich syrup.
 3. The process of claim 1 furtherincluding the step of crystallizing the maltitol rich syrup in order toobtain a crystallized maltitol.
 4. The process of claim 1 furtherincluding the steps of: (a) crystallizing the maltitol-rich syrup; (b)carrying out molecular sieving of the crystallization mother liquors soas to obtain a maltitol-rich fraction and a maltitol-poor fraction; (c)recycling said maltitol-rich fraction upstream of the crystallizationstep; (d) carrying out acid and/or enzymatic hydrolysis of saidmaltitol-poor fraction; (e) carrying out hydrogenation of saidhydrolyzed maltitol-poor fraction.
 5. Crystallized maltose obtained bycrystallizing a maltose-rich syrup as obtained according to claim
 1. 6.Maltitol-rich syrup obtained by hydrogenating a maltose-rich syrup asobtained according to claim
 1. 7. Crystallized maltitol obtained byhydrogenating a maltose-rich syrup as obtained according to claim 1 andthen crystallizing the thus obtained maltitol-rich syrup. 8.Crystallized maltitol obtained by hydrogenating a maltose-rich syrup asobtained according to claim 1 and then crystallizing the thus obtainedmaltitol-rich syrup.
 9. A process for the preparation of a maltose-richsyrup comprising the successive steps of: (a) carrying out liquefactionof a starch milk; (b) carrying out saccharification of the liquefiedstarch milk in the presence of a β-amylase; (c) carrying out molecularsieving of the liquefied and saccharified starch milk so as to collect afraction enriched in maltose and a fraction enriched in glucose; (d)bringing said fraction enriched with maltose into contact with amaltogenic α-amylase and at least one debranching enzyme selected fromthe group comprising pullulanases and isoamylases in order to obtain amaltose-rich syrup; and (e) crystallizing the maltose-rich syrup inorder to obtain a crystallized maltose.
 10. The process of claim 9further including the step of hydrogenating the maltose-rich syrup inorder to obtain a maltitol rich syrup.
 11. The process of claim 9further including the step of crystallizing the maltitol rich syrup inorder to obtain a crystallized maltitol.
 12. The process of claim 9further including the steps of: (a) crystallizing the maltitol-richsyrup; (b) carrying out molecular sieving of the crystallization motherliquors so as to obtain a maltitol-rich fraction and a maltitol-poorfraction; (c) recycling said maltitol-rich fraction upstream of thecrystallization step; (d) carrying out acid and/or enzymatic hydrolysisof said maltitol-poor fraction; and (e) carrying out hydrogenation ofsaid hydrolyzed maltitol-poor fraction.
 13. Crystallized maltoseobtained by crystallizing a maltose-rich syrup as obtained according toclaim
 9. 14. Maltitol-rich syrup obtained by hydrogenating amaltose-rich syrup as obtained according to claim 9.